Appendixb; Ex1629 Filtering; Introduction; Analog Anti-Aliasing Filter - VTI Instruments EX1629 User Manual

EX1629 F
ILTERING
I
NTRODUCTION
The diagram below details the filter chain present in the EX1629 channels, which contains both
analog and digital components. These components are discussed sequentially in the following
sections.
Analog
Ant-Aliasing
Filter
(1-pole RC)
where f = input frequency to FIR decimator, f
so

Analog Anti-Aliasing Filter

The analog anti-aliasing filter consists of a single-pole RC filter with R = 5.62 kΩ and C = 470 pF,
which has a -3 dB point of f
The rejection at 6.25 MHz (the ADC sigma delta modulator sampling rate) is:

EX1629 Filtering

ADC
ADS1271
FIR
6th order
100dB stopband
attn.
modulator
ripple=0.005dB
F
IGURE
= 1/(2π*RC), or 60.254 kHz.
c
1
f
= -40.52426 dB
f
1
2
f
c
A
PPENDIX
FPGA
CIC
50 kSa/s
(R=1-10000,
N=5, M=1)
= user sample rate
s
B-1: EX1629 F C
ILTER HAIN
www.vtiinstruments.com
B
C6713
DSP
Butterworth/
CIC
f
f
compensation s
so
Bessel IIR
filter and FIR
filters with
decimation
variable fc
filter
315